Common Egg Cockle (also known as the Giant Atlantic Cockle)
Phylum: Mollusca, Class: Bivalvia, Order: Cardiida, Family: Cardiidae, Genus: Dinocardium, Species: Dinocardium robustum · Cardiidae (Cockle family) · Bivalve (two-shelled), whole valve, fan/heart-shaped profile.
Species
Dinocardium robustum
Shell Type
Bivalve (two-shelled), whole valve, fan/heart-shaped profile.
Family
Cardiidae (Cockle family)
Size
Approximately 2 to 2.5 inches wide, which is common for a juvenile or medium-sized specimen. Adults of this species typically range from 3 to 5 inches.
Color & Pattern
Predominantly off-white to cream with faint brownish-yellow mottling characteristic of weathering. The natural color pattern of this species typically features reddish-brown zigzag bands or spots on a lighter background, which are faded or bleached in this particular specimen due to sun exposure.
Rarity
Common, frequently found along beaches in the Southeastern United States.
Habitat
Shallow subtidal and intertidal zones, buried just beneath the surface of clean sand bars, mudflats, and near-shore marine environments.
Geographic Range
Western Atlantic Ocean, from Virginia south through Florida, the Gulf of Mexico, and the Caribbean.
Description
A sturdy, inflated bivalve shell featuring prominent, regular radial ribs extending from the umbo to the scalloped margin. The exterior surface has strong sculptural ribs numbering around 32 to 36, creating a deeply corrugated edge. The shape is robust and heart-like when both valves are joined, though this specimen is a single isolated valve.
Key Features
Heavy, inflated valves with numerous (typically 32-36) prominent radial ribs, an asymmetrical oval-to-subcircular outline, and a distinctly toothed or scalloped ventral margin where the ribs terminate.
Collector Value
Low to moderate commercial value. While widely collected and very popular among amateur beachcombers, pristine, brightly patterned large adult specimens hold more value for specialized display collections.
Condition Notes
Fair to Good condition single valve. The shell is structurally intact with well-defined ribs, but it shows significant sun-bleaching with the loss of its vibrant original brown markings and minor wear along the outer margin.
Interesting Facts
Cockles are capable of active locomotion using a powerful, muscular, axe-shaped foot that allows them to leap or dig rapidly back into the sand when uncovered by waves.
Ecological Role
Serves as an important benthic filter feeder, cleaning the water column by consuming microscopic plankton. It is an important food source for marine carnivores including predatory gastropods, fish, and shorebirds.
Similar Species
Magnum Cockle (Vepricardium magnum), which tends to be more elongated and features sharper spines or scales along the ribs.
Beach Finding Tips
Look along high-tide wrack lines on ocean-facing sandy beaches after storms or heavy wave action. Single valves are frequently cast ashore.
Notes
South Carolina